Fridges contain harmful Chlorofluorocarbons (CFCs) and must be disposed of safely.
Your local authority recycling department can tell you if there is a disposal scheme in your area. Try the postcode search on www.recyclenow.com to find your nearest service.
If it is in good working order there are also community organisations who accept donations of used white goods, try the Furniture Reuse Network or the British Heart Foundation for more information. Of course you can always ask family, friends and neighbours if they have a use for it or find a new home for it on Freecycle.